This invention pertains to an improvement on a laminate suitably used for an insulation base material of a printed wiring board, a glass fiber woven fabric used for a laminate base material and a printed wiring board having a laminate as an insulation base material.
Of late, there has been remarkably required an electronic device having compactness and multi-function, which has been accomplished by providing a printed wiring board for the electronic device with higher packaging density. Furthermore, the parts packaged in the printed wiring board have been lighted, thinned and shortened, which causes them to have a lower coefficient of thermal expansion.
In a prior art, an insulation base material for a printed wiring board comprises a laminate produced by preparing glass fiber woven fabrics as base material formed of warps and wefts, both of which are of E glass yarn and impregnated with thermo-setting resin and dried to form prepregs and then superposing them one upon another while they are heated and pressed. Such a laminate has a coefficient of thermal expansion of about 16 ppm/.degree.C. With parts of low coefficient of thermal expansion packaged in such as insulation base material for the printed wiring board, thermal stress will be applied to the soldered joints of the printed wiring board due to a difference of coefficient of thermal expansion between the packaged parts and the insulation base material. As a result, the soldered joints tend to have cracks provided therein. More particularly, if ceramic packages or thin small outline packages (TSOP) having a coefficient of thermal expansion of 8 ppm/.degree.C. or less than will be mounted on the aforementioned insulation base material, cracks in the soldered joints will be hardly avoided.
If glass fiber woven fabrics formed of warps and wefts of T glass yarn are used as base material which is to be impregnated with thermosetting resin, then there will be produced a laminate having a coefficient of thermal expansion of 8 ppm/.degree.C. or less than. However, such a laminate disadvantagesouly has a poor drill workability.